1. Field of the Invention
This invention relates to a wind turbine and to a method of operation thereof where the wind turbine has a variable speed rotor and a plurality of generators, the wind turbine being controlled by a controller to add more generators at higher speeds and to shut down generators at lower speeds.
2. Description of the Prior Art
It is known to have wind turbines where the speed of a rotor is maintained substantially constant despite changing wind speeds by means of a gear box. However, gear boxes are expensive and have been known to fail prematurely, thereby resulting in down time for the wind turbine as the gear box is replaced or repaired. Some previous wind turbines have braking systems on the blades to maintain the blades at a substantially constant speed despite changes in the wind conditions. However, braking systems often become worn and require replacement. Further, braking systems can be an inefficient way to operate a wind turbine because of the energy expended to operate the braking system to maintain constant speed. Yaw controls and pitch controls are also known to be used on wind turbines to assist in operating the turbine at a substantially constant speed. The purpose of operating the previous turbines at a substantially constant speed is to be able to produce AC current at the output of the turbine, the AC current having a frequency that allows the output power to be transmitted into a grid.